Generic electrohydraulic assemblies are employed in motor vehicles to a large extent. The range of functions of electrohydraulic assemblies of this type is constantly increasing. This is because new tasks such as wheel-individual brake control, cruise control and collision avoidance control, hill holders (hill descent control) or brake disc dehumidification due to the automatic application of brake pads add to the conventional tasks such as ABS, ESP, and brake assist systems.
With the range of functions increasing, also control operations become more frequent, which are related to activities of the supply devices. One supply device per brake circuit is provided in conventional assemblies, being primarily used for the return delivery of hydraulic fluid discharged at the side of the wheel brakes or for the pressure increase in wheel brakes. However, the activity of the supply devices entails reactive effects such as pedal vibrating due to pressure surges or acoustic trouble due to structure-borne noise.
To eliminate drawbacks in comfort it has already been considered implementing a gear pump in an electrohydraulic brake system. In systems of this type, the operator is uncoupled from the hydraulic actuation, and actuation takes place by-wire. The supply device (gear pump) serves to charge a high-pressure accumulator so that pedal reactions are omitted.
Another problem refers to the fluid behavior at extreme temperatures, however. This is because the hydraulic medium ‘brake fluid’ is extremely viscous at low temperatures, while it is mobile at high temperatures. Both extremes represent a special challenge.